Images for the six stamps were illustrated by Stroud-based artist Andrew Davidson.
They all show traditional red-coloured postboxes, ranging from smaller ones mounted on a post or in a wall to a large one with a double posting slot.
Each stamp features a cypher from the six monarchs of the last 100 years.
Mr Davidson, who has worked on more than 12 stamp issues for Royal Mail, said: "Knowing my illustrations on the 2018 Christmas stamps will be winging their way around the world delivering season's greetings to friends and family gives me a real sense of festive joy."
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As is usual, religious Christmas stamps of the Madonna and Child in first class and second class rates will also be available from post offices.
The Christmas stamps are on sale from Thursday, with recommended posting dates of December 18 for second class, December 20 for first class and December 22 for special delivery.